Image diagnostic systems have been used for diagnosing arteriosclerosis, for preoperative diagnosis upon coronary intervention by a high-performance catheter such as a dilatation catheter (i.e., balloon catheter) or stent, and for assessing postoperative results.
Examples of these image diagnostic systems include intravascular ultrasound (IVUS) imaging systems. In general, the intravascular ultrasound imaging system is constructed to control an ultrasonic transducer to perform radial scanning within a blood vessel, to receive a reflected wave(s) (ultrasound echoes) reflected by biotissue (e.g. the blood vessel wall) by the same ultrasonic transducer, to subject the reflected waves to processing such as amplification and detection, and then to construct and display a tomographic image of the blood vessel on the basis of the intensities of the received ultrasound echoes. An example of such a system is described in JP-A-H06-343637.
In addition to these intravascular ultrasound imaging systems, optical coherence tomography (OCT) imaging systems have been developed in recent years for use as image diagnostic systems. In an OCT imaging system, a catheter with an optical fiber incorporated therein is inserted into a blood vessel. The distal end of the optical fiber is provided with an optical lens and an optical mirror. Light is emitted in the blood vessel while radially scanning the optical mirror arranged on the side of the distal end of the optical fiber, and based on light reflected from biotissue forming the blood vessel, a tomographic image of the blood vessel is then constructed and displayed. An example of this system is described in JP-A-2001-79007.
Improved OCT imaging systems have been proposed in recent years which make use of a wavelength swept light source.
As mentioned above, there are a variety of different image diagnostic systems which use different detection principles. Nonetheless, they are all generally characterized in that a tomographic image (i.e., cross-sectional image) is constructed and displayed by performing radial scanning with a probe. In each of these image diagnostic systems, an increase in axial scanning speed by the realization of faster radial scanning can, therefore, bring about a merit that the time for a diagnosis by the image diagnostic system can be shortened.
However, when a probe is rotated at high speed, for example, as shown in FIG. 9A, when a probe is operated toward the distal direction (i.e., the periphery) within a body cavity with a catheter 11 that is bent at a distal end portion thereof, an ultrasonic transducer unit 12 arranged at the tip of the probe may pierce through the catheter 11, as illustrated in FIG. 9B, thereby breaking the catheter 11 and/or damaging a blood vessel or the like.
As a diagnosis is generally performed by moving a probe toward the user (i.e., in a direction away from the distal direction in the body cavity), such a problem does not typically occur. In some instances, however, a probe may be moved automatically or manually toward the distal direction to finely adjust a measurement-initiating point while confirming tomographic images in real time. Further, with the probe kept rotating, the probe may be moved to a most distal end toward a distal direction to repeat a measurement. When the rotation speed of the probe is fast, such a problem can occur upon movement of the probe toward the distal direction within a body cavity.